Bipolar Demi Lovato Talks Cutting, Eating Disorders

No one was more surprised to learn that DemiLovato is bipolar than the singer herself.

"I had no idea that I was even bipolar until I went into treatment," the Disney star reveals on 20/20 (airing April 22 at 10 p.m. EST). "I was actually manic a lot of the times that I would take on workloads, and I would say, 'Yes, I can do this, I can do this, I can do this.' I was conquering the world, but then I would come crashing down, and I would be more depressed than ever."

Teased for her weight as a kid, Lovato developed an eating disorder that turned into a lifelong struggle with food. "That's kind of what I've been dealing with ever since," she admits. "I was compulsively overeating when I was eight years old. So, I guess, for the past 10 years, I've had a really unhealthy relationship with food."

Lovato's family helped her seek professional help to treat her bulimia, but the singer's depression only worsened when she began cutting herself at the age of 11.

"It was a way of expressing my own shame, of myself, on my own body," the Princess Protection Program star says. "I was matching the inside to the outside. And there were some times where my emotions were just so built up, I didn't know what to do. The only way that I could get instant gratification was through an immediate release on myself."

The dangerous coping mechanism continued throughout Lovato's teen years. When she began touring with the JonasBrothers in the summer of 2010 -- alongside her ex, JoeJonas, no less -- Lovato once again using food as a means of control.

"I was performing concerts on an empty stomach," she said. "I was losing my voice from purging. I was self-medicating. I was not taking medication for depression, and I literally was so emotionally whacked out that I took it out on someone that meant a lot to me."

During the South American leg of the Camp Rock 2 tour, Lovato physically struck one of her backup dancers, AlexWelch. "I take 100 percent full responsibility," Lovato now says. "I feel horrible. She was my friend."